Well Rachel is technically a ninja isn't she?
No! She's not even "Human".
Technically she's a vigoorian, altough that's not very different from any other humans lol, just different lineage.
She received the "blessing of blood" or whatever it was called, giving her superhuman strenght, reflexes etc.
She also can use some incredible tools and a powerful scythe-like thing.
She's a "demon hunter" or whatever she was called?
In theory judging from Ninja Gaiden Sigma 1 and then 2 she's able to use some magic spells as well but I'm not sure if we should consider those things canon, since there's not the hand of Itagaki behind.
She definitely cannot overpower Hayabusa, but then again Hayabusa is on a league of his own even among Ninjas.
Dunno what she could do against Kasumi/Ayane/Hayate, but I have a feeling while she would definitely be an interesting match, the latter 3 would definitely win in the end.
I'm having issues in measuring the power of Momiji, in theory she's really really strong. Shouldn't be that far behind (or ahead) of those 3 ninjas.
But back to Bayman and Christie, I think Christie would put up a better fight because she's fast. Haven't yall noticed that? Christie isn't a ninja but she's like "I got hands too!". Plus Christie has no fear, for some odd reason, because remember she was willing to fight Ayane AND Ryu in DOA4? Crazy Bitch. But yea, she would put up a better fight than Bayman.
Good points.
Plus let's nto forget that she's deeply involved with Donovan, who knows, she might have some secrets.
I still do believe she has no chances against ninjas, but again, she's definitely gotta be more powerful than the majority of other DoA characters.
Of course we haven't mentioned Boss characters of DoA, goes without saying that they would all pose a serious threat to all the ninjas. Two of them bosses actually *ARE* Ninjas lol.